I'm very confused by how you nitpick your timeline here. Between 2002-2015 you have a 2.6 year average. The last Bethesda RPG was in 2015, so we're around that timeline. 3 years. Maybe 4 depending on when TES6 comes out. You can't just randomly pick 2011 and say "It's been one RPG in 7 years" No, technically it's 2, you have to count the beginning mark Skryim - so that's 3.5 years. One extra year per your own acceptable average.
I think, again, this is just selective outrage and speculation. I'll speculate in the other direction and say that it's not these new directions that is having a detrimental affect (barely) on acceptable release timelines and say it's all those other titles I mentioned. You can make a distinction between BGS and all the other devs under BS, but even BS says that they and BGS and Zenimax are all one and the same. Just like with Valve and when Steam blew up, they've got a lot more stuff to handle on top of developing everyone's favorite games. They have to balance resources, and that doesn't just mean whatever devs technically assigned to the BGS group, but marketing, legal, etc. So when as a company you have these huge franchises like Doom and Wolfenstein and Dishonored and smaller hits like Prey and Evil Within, you have an obligation to them and all your other studios to balance things, dedicate resources to each release, and space things out. That's my take on it. And given how well BS has handled almost every franchise it's bought, I'm quite happy waiting longer in between releases. But I love FPS games more than RPGs so having them flood me with all those franchises in between Fallout is great for me. I can see how RPG nerds would cry about it.